The invention relates to a nuclear reactor installation comprising a reactor pressure vessel made of steel and which is surrounded by a concrete wall forming an annular space around the vessel, this wall being required both as a biological shield and as a containment for the vessel. To protect the concrete wall against excessive thermal stressing, thermal insulation surrounds the vessel in the annular space and a coolant-conductive layer is positioned between the thermal insulation and the concrete wall so that a coolant can be passed through this layer. The components described completely fill the annular space between the vessel and the concrete wall when the pressure vessel is thermally expanded by reactor operation, thus providing zeroexcursion rupture safeguarding of the vessel, the various components in the annular space being intended to have high compressive strength.
The thermal insulation which is next to the vessel, is designed for removal when the reactor is shut down and the vessel is cold, to permit external inspection of the vessel. Therefore, the insulation is made from concrete segments of large size and which may be lifted to clear an annular space around the vessel, using the usual containment crane. To provide the coolant-conductive layer, a sheet steel skin can be spaced from the concrete wall and filled with loose small particles such as steel balls, ceramic spheres, gravel or the like, which when compacted, becomes resistant to compression stress as required when the reactor is thermally expanded. However, this compaction required to carry the compression stress, via the loose particles, unfortunately produces a densification causing a high flow resistance or a coolant flow resistance to a coolant flow through the layer. If air is used, undesirably high air pressure are involved.
At the same time the loose particles can be poured between the skin and the concrete wall during erection of the installation, and this is a desirable advantage.